The present invention relates to a circuit board that comprises a board on which electrodes, wirings and through-holes are formed and is used for connecting to an actuator of an inkjet head, for example, and relates to an inkjet head.
The inkjet head records images, such as letters and figures, on recording paper by ejecting ink from nozzle holes while moving relative to the recording paper. The inkjet head has a plurality of rows of nozzle holes arranged in a line along the moving direction of the recording paper, and incorporates an actuator (for example, a piezoelectric element) for ejecting the ink from each nozzle hole, an IC chip for driving the actuator, and a circuit board for connecting the actuator and the IC chip (see Japanese Patent Application Laid-Open No. 2004-114609).
FIG. 1 is a plan view showing the structure of a conventional circuit board, and FIG. 2 is a cross sectional view along the VI-VI line of FIG. 1. A plurality of electrodes 31, 31, . . . having an oval shape in the plan view are formed on one surface of a flexible sheet 1 made of an insulating film. The electrodes 31, 31, . . . are lined in the width direction of the electrodes 31, 31, . . . to form electrode rows 130, 130, . . . , and further the electrode rows 130, 130, . . . are arranged in a longitudinal direction of the electrodes 31, 31 . . . so that the electrodes 31, 31, . . . included in adjacent electrode rows 130 and 130 form a zigzag pattern.
A wiring 32 with a width shorter than the length in a width direction (hereinafter referred to as the width) of the electrode 31 is connected to each electrode 31 at one end portion in the longitudinal direction, runs in the arrangement direction of the electrode rows 130, 130, . . . to pass between the electrodes 31 and 31 adjacent to each other in the row direction, and is connected to an IC chip, not shown.
On one surface of the flexible sheet 1, an insulating layer 11 is formed to cover the electrodes 31, 31, . . . and the wirings 32, 32, . . . .
Moreover, in the flexible sheet 1, through-holes 10, 10, . . . having an oval shape in the plan view and a longitudinal direction equal to the longitudinal direction of the electrodes 31, 31, . . . are formed at the positions where the electrodes 31, 31, . . . are formed. The opening area of each through-hole 10 in one surface of the flexible sheet 1 (the surface where the electrodes 31, 31, . . . are formed) is smaller than the area of the electrode 31. On the other hand, the opening area in the other surface is larger than the above-mentioned opening area and is substantially equal to the area of the electrode 31.
An electrically conductive brazing filler metal (solder) H is deposited thicker than the thickness of the flexible sheet 1 onto each electrode 31 from the other surface of the flexible sheet 1 through the through-hole 10, and the electrode 31 is connected, for example, to an individual electrode 41 corresponding to an individual nozzle hole (not shown) of an actuator 4 through the deposited solder H.